1. Field of the Invention
The present invention relates to an image forming apparatus such as a facsimile machine, printer, and copying machine, and particularly to a sheet conveying apparatus capable of preventing self-oscillation of a conveying roller.
2. Description of the Background Art
As disclosed in Japanese Patent Application No. 2974911 and Japanese Patent Application Laid-Open No. H9-25017, for example, in an image forming apparatus such as a facsimile machine, printer, and copying machine, there has been conventionally used a sheet conveying apparatus which is installed in a place for conveying a set sheet of script to a reader or a place for conveying a sheet of paper stored on a paper feed tray to an image forming section. Further, the sheet conveying apparatus is installed in not only these places but also a place for conveying a sheet discharged to a catch tray to a predetermined location.
Such a sheet conveying apparatus is constituted from a pickup roller which functions as a conveying roller for conveying a sheet, an arm in which the pickup roller is attached rotatably to one end thereof and a spring is attached to the other end thereof, and a sheet supporting plate which faces the pickup roller with a sheet therebetween. The arm is attached rotatably to an axis extending from the apparatus main body, and the pickup roller is capable of oscillating in a top-to-bottom direction. Furthermore, the pickup roller is brought into contact with a sheet by the spring at a predetermined pressure. When conveying a sheet which is set on the sheet conveying apparatus, the pickup roller rotates in a sheet conveyance direction and, with this rotation, the sheet is conveyed in a paper feed direction by frictional force between the pickup roller and the sheet.
However, in the prior art, there was a problem that, when the number of sheets set on the sheet conveying apparatus decreases after being conveyed, delay of sheet conveyance occurs. Particularly, when the number of set sheets decreases below twenty, the pickup roller oscillates by itself, and the contact pressure between the pickup roller and the sheet is reduced. As a result, the frictional force between the pickup roller and the sheet also decreases and the pickup roller slips on the sheet. As a result, it was discovered that the distance of conveyance performed by the pickup roller decreases, causing delay of sheet conveyance.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Application Laid-Open No. 2002-068505 and Japanese Patent Application Laid-Open No. 2003-155129.